In EP-A-1 291 189, herein incorporated by reference in its entirety for background information only, a double sided color proofing apparatus uses rolled web material as printing stock and is further provided with a web feed device, a tumbler unit for turning the receiving medium and a alignment sensing and correction system. The web feeding device is provided with a decurling roller to reduce curl of the medium when the paper is fed from the paper roll. However is was found that, even when using the decurling roller, not all curl can be removed leaving a problem of residual curl, even after decurling of the medium. Especially when making very large format printers residual curl can still pose severe problems and can lead to a misfeed of the cut sheet and paper jam during functioning of the printer.
Another problem is that curl is depending upon relative humidity of the paper stock. There have been reports of working environments having a relative humidity of 10% during weekend days when conditioning systems of the print room are switched off. As the working week is started conditioning systems are switched on but the paper roll can not be rehydrated in time to avoid functioning problems.
There is clearly a need for an improved printing apparatus capable of avoiding problems due to residual curl of the print medium. There is a need for printing apparatus capable of handling media having considerable curl. This would put less restrictions on the quality and conditioning of the paper.